Thermostatic switch



July 12, 1932. SCHERBlUS 1,867,384

THERMOSTATIC SWITCH Filed May 25, 1929 g- 9. Fig.2.

Invenbcn i AYth U1" Scherloius,

His Attorneg.

Patented July 12, 1932 UNITED STATES PATENT OFFICE ARTHUR SCHERBI'US, OF BERLIN, GERMLANY, ASSIGNOR TO GENERAL ELECTRIC COM- PANY, A. CORPORATION OF NEW YORK THERMOSTATIC SWITCH Application filed May 23, 1929, Serial No. 365,437, and in Germany September 7, 1928.

This invention relates to thermostatic switches and the like, and has for its object the provision of simple and reliable means for adjusting the temperature setting and for abruptly separating the switch "contacts.-

For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 shows a thermostatic switch provided with temper- 10 ature adjusting means embodying my invention; Figs. 2 and 3 show modifications of the device shown in Fig. 1; Fig. 4 shows a thermostatic switch provided with means for abruptly separating the contacts; while Figs.

in Fig. 4.

Re erring to Fig. 1 of the drawing I have shown my invention in one form as comprising a bimetallic thermostatic strip which is secured at one end by screws 11 to a supporting frame 12. The free end of the thermostat is provided with a knife-edge 13 and an oppositely disposed knife-edge 14 is provided on the support 12. Between these two knife-edges, which constitute bearings, an inverted U-shape spring member 15 is provided. As shown, the lower ends of the spring are provided with bearing depressions 16 and 17 which fit on the knife-edge bearings 13 and 14 respectively, whereby the spring exerts a pressure on the end 0 the thermostat in the direction of the lengt or longitudinal axis of the thermostat. The spring 15 carries a contact arm or lever 18 which is secured at one end by suitable rivets to the upper transverse portion 19 of the spring. This contact arm 18 carries a contact 20 which engages under certain temperature conditions with a stationary contact 21 mounted on an arm 22 secured to the frame 12. Electrical power is supplied to the switch by a conductor 23 secured to the frame 12 whereby an electrical connection is made through the various parts to the contact 20, and by a conductor 24 leading to the stationary contact 21,.which contact is suitably electrically insulated from the supporting arm 22. The supporting arm 25 forming a part of or secured to the frame 12 is rovided at its end with a stop 26 with whic cooperates a 5 and 6 are modifications of the form shown stop 27 secured to the arm 18 whereby the upward movement of the arm is limited. This arm 25 also is provided with a calibrating screw 28 secured to the arm in screw threaded relation therewith and extending downward through a suitable aperture provided for it in the arm- 18. This screw 28 is located at a point near the end of the thermostat and extends substantially at right an- 'gles to the normal position of the thermostat. The calibrating screw engages one end of a helical spring 29, the other end of which presses up on the thermostat 10 at a point near its free ends. 7

In the operation of the device, upon an increase in temperature of the thermostat its free end bends upward in the direction of the arrow 30 thereby separating the contacts 20 and 21. It will be understood, that the efleot of the spring 15 is to give the contact arm 18 a snap action, as described andclaimed in Reissue Patent 16,654 to Lewerenz dated June 14, 1927. Certain features including the U- shape spring 15 are described and claimed in Patent No. 1,743,073 to A: H. Simmons. By means of the screw 28 thespring 29 may be tightened which causes the contacts 20 and 21 to be separated at a higher temperature. By turning this screw 28 so as to loosen the spring 29 the thermostat can be set to operate at a lower temperature.

In the modified form shown in Fig. 2 a fiat spring 31 is provided for effecting the tem perature adjustment. One end of this spring is secured, as by a rivet 32, to the free end of the thermostat 33. The spring extends back toward the flexed end of the thermostat in longitudinal relation therewith and cooperates at its other end with the adjustment screw 34 which is secured to an arm 35 attached in turn to the frame 36. -When the thermostat moves up or down there is obvi ously a tendency for the spring 31 to slide or move across the point of contact with the screw 34. This movement would interfere with the proper operation of the device by reason of the resulting friction. In order to prevent this movement the end of the screw 34 is made pointed and arranged to rest in a depression 37 in the end of the spring. Also the spring itself is provided with an upward bend 38 by reason of which the spring has a certain amount of yielding movement in the direction of its length. Instead of a depression in the end of the spring a hole may also be used for the end of the adjustment screw. This arrangement is shown in Fig. 3, wherein calibrating screw 38 is provided with a pin 39 which extends through a hole in the spring 40.

In Fig. 4 I have shown an arrangement for getting a more pronounced quick separation of contacts whereby arcing is prevented. In this figure the arrangement of the bar thermostat 41, the spring 42, and the contact arm 43 is similar to that previously described in connection with Figs. 1 and 2. The electrical contact 44 carried by the arm43 is movably secured to the arm however. As shown, this contact is mounted on the lower end of a pin 45 which extends upward into a bore or recess in a member 46 secured to the end of the arm 43. A pin 47 is secured to one side of the pin 45 and extends through an oval shape hole 48 in the guide" member 46. This hole is elongated in the direction of the length of the pin 45, so that the pin 45 has a limited freedom of movement in the member 46 determined by the length of the hole 48.

In the operation of the device shown in Fig.

'4, when the thermostat 41 is heated its free end moves upward carrying with it the contact arm 43. This movement does not immediately lift the contact 44, however, due to the freedom of movement of the pin 47 in the slot 48. However, due to, the effect of the spring 42 the movement of the thermostat and hence of the lever 43 becomes increasingly faster as it proceeds so that the contact arm is accelerated to a considerable speed before the pin 47 is engaged by the lower end of the slot 48 and the contact 44 is lifted. This speed of movement of the contact arm independently of the contact 44 results in the contact 44 being ultimately separated from its cooperating contact with a jerk whereby a quick separation is effected.

Another advantage is that the forces resulting from such a jerk of hammer blow are many times larger than the normal force, as in the case of a hammer. This force due to the jerk will separate the contacts even in case a small amount of fusing has taken place betwen them, in addition to extinguishing the are very quickly and thereby appreciably reducing the wear on the contacts.

The use of the contact arm 43 is particularly advantageous because the increased displacement due to the use of the contact arm makes it possible to separate the contacts with a smaller force.

The specific arrangement of Fig. 4 is main- 1y feasible when the switch is always maintained in the same upright position in which the contact pin 45 is vertical so that the contact 44 is held in engagement with the lower contact by its own weight and the weight of the pin. In case the switch is to be used in various positions I provide a weak spring which presses the contacts against each other as shown in Fig. 5. Referring to Fig. 5, a spring arm 49 is provided having one end secured to the contact arm 50 adjacent the spring 51. The other end of the arm 49 engages a flange 52 on the lower end of the contact pin. For example, the arm 49 may be forked at its end so as to embrace the contact pin. The arm is arranged so as to exert a light pressure in a direction to move the contact pin out of its guide and seat the pin 53 in the lower end of the oval slot 54.

As shown in Fig. 6 the arrangement of Fig. 5 may be reversed, one contact 55 being rigidly secured to the switch arm 56 and the other contact 57 being movably secured to the stationary support 58 in the manner previously described in F ig. 5 in connection with the contact arm 50. This contact 57 is forced upward by a spring 59.

The construction shown in Figs. 4, 5 and 6 are, of course, only examples of possible constructions of the invention. The actual constructions can be carried out in different ways, the essential feature however being that at least one of the two contacts has a limited freedom of movement with respect to its supporting part.

What I claim as new and desire to secure by Letters Patent of the United States is 1. A thermostatic switch comprising a bimetallic strip having one end fixed and its other end arranged to move from one position to another in response to changes in temperature, resilient means cooperating with said strip so as to give said free end a snap action, a second resilient means cooperating with the free end of said strip and means for adjusting said second resilient means to vary the temperature setting of said device.

2. A thermostatic switch comprising a bimetallic thermostatic strip arranged to move from one position to another in response to changes in temperature, resilient means for giving said strip a snap action, switching means actuated by said strip, a second resilient means cooperating with said thermostat so as to oppose its movement in one direction, and means for adjusting said second resilient means so as to Vary the temperature setting of said device.

3. A thermostatic switch comprising a bimetallic thermostatic strip having one end fixed and its other end free to move from one position to another in response to changes in temperature, resilient means cooperating with the free end of said strip so as to give said strip a snap action in moving from one position to another, a contact arm carried by said resilient means, said arm being provided with a contact, a stationary contact arranged to be engaged by said first contact, a spring cooperating with the free end of said strip so as to oppose its movement in one direction, and

i means for varying the tension of said spring so as to change the temperature setting of the device.

In "witness whereof, I have hereunto set my hand this 7th day of Ma 1929.

ARTHUfi SGHERBIUS. 

